1. Field of the Invention
This invention relates to a production method of a ceramic catalyst body used for an exhaust gas purification catalyst of an automobile engine, and so forth.
2. Description of the Related Art
Cordierite having high thermal impact resistance has been used widely as a ceramic support in ceramic catalyst bodies according to the prior art. Generally, after a surface of a support formed of cordierite molded into a honeycomb shape is coated with γ-alumina, a precious metal catalyst is carried thereby to produce a ceramic catalyst body (refer to Japanese Examined Patent Publication (Kokoku) No. 5-50338).
The reason why the coating layer is formed is because the surface area of cordierite is relatively small and cannot as such sufficiently support a necessary amount of the catalyst. When the surface of cordierite is coated with γ-alumina having a high specific surface area, the surface area of the support can be increased.
However, coating of the surface of the support with γ-alumina invites the problem that a thermal capacity increases due to the increase of the weight. To quickly activate an exhaust gas purification catalyst, studies have been made in recent years to reduce the thickness of a cell wall of the support and to lower the thermal capacity. Formation of the coating layer lowers the effect of the drop of the thermal capacity.
Furthermore, disposition of the coating layer invites the problems that a coefficient of thermal expansion becomes great and that a pressure loss increases because an open cell area in the honeycomb support decreases.
Fine pores of the coating layer are susceptible to damage due to heat and the surface area decreases with time. The catalyst physically adsorbed into the fine pores is entrapped inside with the decrease of the surface area and the catalyst amount decreases, thereby lowering purification efficiency.
In view of these problems of the prior art described above, the present invention aims at providing a production method of a ceramic catalyst body that can directly support a catalyst on a ceramic support and that does not easily undergo thermal degradation.